- Luminous Efficacy Definition: Luminous efficacy is the measure of how much light a lamp produces per unit of power consumed, defined as lumens per watt.
- Energy Efficiency: Fluorescent lamps are more energy-efficient than incandescent lamps, with higher luminous efficacy.
- LED Efficiency: LED lamps can achieve up to 200 lumens per watt, making them highly efficient light sources.
- Correlated Colour Temperature (CCT): CCT indicates the color of light emitted by a lamp, measured in Kelvin, with different ranges for warm, neutral, and cool white light.
- Colour Rendering Index (CRI): CRI measures how accurately a lamp reproduces colors compared to natural light, with incandescent and halogen lamps having a CRI of 100.
Luminous Efficacy
Luminous efficacy tells you how much visible light a lamp emits for each watt of electric power it uses. It is luminous flux in lumens divided by power in watts, so the unit is lumens per watt (lm/W). A higher value means that the lamp produces more light for the same electrical input. The result varies by type of lamp and by the driver, optics and operating conditions included in the measurement.
Incandescent, fluorescent and LED lamps have different efficacy ranges. Incandescent lamps convert more input power to heat, while fluorescent lamps usually produce more lumens per watt. Current LED products generally provide the highest lamp efficacy, but the exact value must come from the product’s measured lumen output and input power.
Correlated Colour Temperature
Correlated Colour Temperature (CCT) is the temperature of the Planckian radiator whose chromaticity is nearest to that of the lamp. It describes the appearance of the emitted light, not the lamp’s physical temperature.
CCT is measured in kelvin (K). A lamp rated at 4500 K has a chromaticity near that of a Planckian radiator at 4500 K. The rating does not mean that both sources have the same spectrum.
Manufacturers commonly describe lamps below about 3000 K as warm white. Their light tends to look more yellow or red than higher-CCT white light, but the label boundaries can vary by product range.
Lamps around 3000 K to 4000 K are often sold as neutral white. Check the stated CCT because a marketing label alone does not define one fixed chromaticity.
Lamps above about 4000 K are often sold as cool white and tend to look bluer than lower-CCT lamps. CCT describes colour appearance, while it does not by itself measure colour rendering.
Colour Rendering Index
An object’s apparent colour can change with the spectrum of the light falling on it. Two lamps with a similar CCT can render the same surface differently because their spectral power distributions differ.
Colour rendering index (CRI) measures how closely object colours under a test source match their appearance under a reference illuminant, after accounting for chromatic adaptation. The general index Ra averages results for eight specified test-colour samples. It is an index, not a fraction. Incandescent and halogen lamps commonly score near 100 because the reference used at their CCT is also Planckian, but CRI should be read from the tested lamp data.
